just looked up the noise by-laws for the City of Vancouver and noted this within them:

“Amplified sound of a radio, television, player or other sound playback device or amplification equipment, or the sound of musical instrument that emanates from a motor vehicle should not be easily heard by someone outside the motor vehicle.”

It’s very specific this part of the by-law thus beware if you are thinking of whipping out your mouth organ. What is the likelihood of someone playing a musical instrument inside a car?

Yet there is no mention of putting your hand on the horn. In other words the car can make music, not the passengers (but the car alarm cannot make music the bylaw covers that)